Please elaborate on the problem you are trying to solve.
Sure, what are all the JSON schema fields and what is possible?
It feels super limited and kinda useless w/out that schema b/c the simple dashboards look terrible imo ;]
Dashboard Studio is intended to be used as a WYSIWYG editor so the underlying JSON is not well documented. That may change as the product matures and gains more sophisticated users such as yourself.
In the meantime, perhaps the documentation at https://docs.splunk.com/Documentation/Splunk/9.0.1/DashStudio/objOptRef is more of what you seek.
Also, feel free to submit feedback on the Dashboard Studio pages to let the docs team know what you'd like to see published.